Knowledge of the pathways of metabolic activation and detoxification of the representative carcinogens, N-2-fluorenylacetamide (2-FAA), benzo(a)pyrene (BaP), and N'-nitrosonornicotine (NNN) has advanced rapidly. It has now become possible to assay for activated and detoxified metabolites from these carcinogens routinely by high pressure liquid chromatography, and to rapidly screen compounds for their potential inhibitory effect (e.g. increase in the formation of detoxified metabolites and/or decrease in the formation of activated metabolites). It is the purpose of this project to discover new inhibitors of chemical carcinogenesis and to establish the structural requirements favoring the action of compounds as inhibitors by examining the changes in the activation and detoxification pathways of the metabolism of 2-FAA, BaP and NNN. A three-tiered screen prior to bioassays will be employed as follows: 1. In vitro assays for metabolites of 2-FAA, BaP, and NNN using liver microsomes prepared from potential inhibitor-treated and control rats. 2. Mutagenicity assays using the S-9 fraction obtained from treated and control rats. 3. Assays for BaP metabolites formed in mouse skin and NNN and 2-FAA metabolites formed in vivo. Only compounds which show promising changes in the first screen will be subjected to the second screen and only those which are confirmed in the mutagenicity assay will be used for the third screen. When a potential inhibitor passes all three screens, bioassays will be carried out. Four categories of compounds have been chosen to be studied in this manner: (1) antioxidants, (2) known modifiers of enzymatic activity, (3) sulfur-containing compounds and (4) structural variants on a known inhibitor, BHA. It is expected that new inhibitors will be discovered in the study of the first three categories of compounds and that structural features necessary for inhibitory activity will be determined by comparing the inhibitory effect of derivatives of BHA.